1. Field of the Invention
This invention relates to an anti-spilling valve for a vehicle fuel tank, more particularly to an anti-spilling valve for installation in the top of the fuel tank of a vehicle, particularly an automobile, for preventing pressure buildup in the tank during normal operation by allowing internal tank pressure to escape to the exterior and for preventing spillage of gasoline to the exterior and reducing the danger of fire when the vehicle overturns or turns sharply.
2. Description of the Prior Art
Japanese Utility Model Public Disclosure Sho 63(1988)-50525 discloses an anti-spilling valve for a vehicle fuel tank comprising a cylindrical valve chamber having an upper cover, closed at the bottom and formed at the center of the upper cover with an upwardly directed exhaust passage for fuel vapor, a connecting pipe formed integrally with the top of the upper cover of the cylindrical valve chamber to extend radially outward and having the upper end of the exhaust passage communicating with its inner end at a right angle, and a float housed in the cylindrical valve chamber to be vertically movable and having on its upper surface a valve head adapted for closing the lower end of the exhaust passage.
The inside diameter of the upwardly directed exhaust passage formed in the upper cover of the cylindrical valve chamber is normally 2 mm and the inside diameter of the connecting pipe whose inner end communicates with the upper end of the exhaust passage at a right angle is normally 4 mm. For integrally forming the upper cover of the cylindrical valve chamber and the connecting pipe integrally of plastic, molten resin is injected into a die provided with a 2-mm vertical core pin for forming the exhaust passage and with a 4-mm lateral core pin for forming the bore of the connecting pipe, the upper end of the vertical core pin and the tip of the lateral core pin contacting each other at a right angle. The injection pressure is set high because low injection pressure may cause short molding. Since the two core pins merely meet each other at a right angle, however, use of a high injection pressure causes resin to pass in between their contacting portions. When this happens, a resin film is formed between the upper end of the exhaust passage and the interior of the end portion of the connecting pipe, resulting in a defective product in which the exhaust passage and the connecting pipe do not communicate. This makes it necessary to press the vertical and lateral core pins onto each other strongly so as to prevent the high-pressure resin from entering between them. When this is done, however, the thin (2 mm) vertical pin is apt to bend, making it impossible to form the exhaust passage.
This invention was accomplished in response to the foregoing circumstances and has as one of its objects to provide an anti-spilling valve for a vehicle fuel tank which enables the exhaust passage to be formed with high reliability and further enables reliable control of the fuel vapor pressure in the fuel tank.
Another object of the invention is to provide an anti-spilling valve for a vehicle fuel tank whose superior sealing property makes it readily installable in a plastic fuel tank.